Most research on the prevention of osteoporosis has been derived from older women. Prevalence is much higher in women than in men due to lower body mass, longer life span, and a precipitous decrease in sex hormones at menopause. However, osteoporosis is a growing concern for men as well as they are now commonly living beyond the age of 75 when hip fracture incidence rates begin to rise exponentially. Physical activity is recognized to be an important component of osteoporosis prevention, yet factors that have been examined in women are typically applied to men without sufficient study to determine how they may differ by gender. Even in women, the duration, intensity, and period of life of activity required for bone health have not been adequately defined. The investigators on this proposal intend to study physical activity and inactivity in relation to the risk of hip fractures due to low or moderate trauma over a twenty-year period in over 46,000 men in the Health Professionals Follow-up Study. Activity will be examined by duration and intensity and will include analyses of walking, moderate and strenuous activities, and sitting. The effects of activity at earlier periods of life, current adult activity, and lifetime activity will also be compared. These same investigators have already examined physical activity in relation to risk of hip fracture in women in the Nurses'Health Study using the same instrument for data collection, the same follow-up procedures for ascertaining incident fractures, and the same biennial assessment of other risk factors, including body weight, diet, smoking, and alcohol consumption. This will allow for gender comparisons of the influence of activity on risk of hip fracture. Clearly, more research is needed on osteoporosis and hip fracture that focuses solely on men. Better knowledge of the effects of physical activity would greatly add to the general advice that is currently available. PUBLIC HEALTH RELEVANCE: In this proposed research, we intend to examine the effects of physical activity and inactivity on risk of hip fractures in men using data previously collected in the Health Professionals Follow-up cohort. Activity factors will include duration, intensity, and period of life. Most of the previous research on osteoporosis and hip fractures has focused on women, and gender differences have not been adequately examined. We intend to compare our results for men with results from our previous research on activity and hip fractures in women. Advice on activity that is specific for men would encourage the expansion of public health messages on osteoporosis to extend beyond the current audience of postmenopausal women to include the growing population of aging men.